DEVELOPERS: add Julien Olivain for package/openmpi

The package has been orphan since commit ee58353 (2018-12-22).

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

DEVELOPERS

@@ -1691,6 +1691,7 @@ F:	package/highway/
 F:	package/libjxl/
 F:	package/octave/
 F:	package/ola/
+F:	package/openmpi/
 F:	package/perftest/
 F:	package/ptm2human/
 F:	package/python-distro/